Cardiac valves, so called heart valves, are found in a number of embodiments made both of wholly artificial materials, such as titanium, pyrolytic carbon or the like, or manufactured from natural tissue of porcine or bovine origin, said materials being treated in a chemical manner so as to obtain desirable properties. All hitherto known back valves for such intended function are associated with severe disadvantages, among which the following may be mentioned.
The designs not based on natural tissue are all made as more or less complicated constructions which result in risk of failure or unsatisfactory function in other ways. Known valves are, furthermore, designed so as to occupy, in an open position, an essential part of the flow cross-section, thus offering resistance to the flow of blood. Many of the known valves are furthermore designed in an asymmetric way with concomitant inconveniences. Finally, it can be mentioned that known valves often are associated with inertia in their opening or closing movement which substantially reduces their efficiency.
U.S. Pat. No. 5,078,739 relates to a cardiac valve said to be capable of replacing any one of the four valves of the heart. This known valve includes a ring having a central opening and two valve flaps arranged to open and close. This construction results in the disadvantage that an asymmetric flow pattern is created with concomitant turbulence and undesired deposits.
U.S. Pat. No. 4,820,299 describes a cardiac valve having three valve elements for opening and closing each provided with a hinge arrangement to the surrounding ring. One part of the hinge arrangement is constituted by a yoke directed inwardly into the flow of blood, whereby disturbances arise in the flow of blood and thereby non-desired deposits of coagulated blood. Furthermore, the construction means that in the open state spaces are formed between the exterior surface of the valve elements and the interior surface of the ring through which blood can flow at the side of the main flow, and also this condition results in non-desired flow profiles creating conditions for deposits in an undesired way.
In PCT-application SE93/00219 there is described a coronary valve, so called heart valve, comprising a sleeve or a ring having a central opening and three flap elements for opening and closing giving the valve the function of a back valve. The flap elements are pivotably connected to the inside of the ring at one end thereof, and each hinge contains a pin or stud which is attached to the ring in a tangentially extending aperture therein. The disadvantage of this known construction is that these pins or studs are arranged in a through-hole in the ring whereby blood can enter into these holes both from the inside and from the outside. Since such blood present around the pin is stationary and not continually replaced problems arise in the form of deposits of coagulated blood and thereby associated problems.